The invention relates to a heat exchanger for cooling air, with a coolant onward-flow connection for supplying liquid coolant for cooling air, a coolant return-flow connection for discharging liquid coolant, a heater for removing ice by melting accumulated ice in the heat exchanger, wherein an electrical heating element for melting accumulated ice is also associated with the heater, and with an operational safety device for preventing overheating of the heater. Furthermore, the invention relates to a heater with a heating element for melting accumulated ice and with an operational safety device for preventing overheating of the heater, as well as a galley for a commercial aircraft, with a receiving space for trolleys and a cooling device for cooling the receiving space, wherein the cooling device comprises such a heat exchanger.
Commercial aircraft comprise galleys in which food and beverages can be prepared, for example heated up, for passengers. In order to also keep perishable food and beverages fresh and palatable for an extended period of time, such galleys comprise one or several coolable receiving spaces in which the food and beverages can be stored, or temporarily stored, in serving trolleys, hereinafter referred to as trolleys.
For cooling, a water-glycol mixture cooled to −9° C. is pumped through a heat exchanger within an air chilling unit (ACU). The above-mentioned value of −9° C. refers to a freely selectable setpoint temperature, set system-internally, relating to the liquid coolant. Other setpoint temperatures are also possible as long as the legally required value of 4° C. for storing food and beverages is maintained. A fan conveys air through the heat exchanger, which cools this air, so that by subjecting the food and beverages in the trolleys to cooled air, said food and beverages are cooled. Due to the low temperatures and the atmospheric humidity contained in the air, ice can form on the heat exchanger, which ice gradually blocks the air flow through the heat exchanger. In a defrosting cycle, such accumulated ice is regularly removed by a heater on the heat exchanger, by means of which heater the accumulated ice is melted. In the case of a malfunction this heater can generate inadmissibly high temperatures and therefore needs to be monitored.
This heater can be designed as a heating mat and can be bonded to a heat exchanger made of aluminium. At one point of the heating mat there is a temperature control fuse which is triggered if a limit value relating to the temperature of the heat exchanger is exceeded, and in this manner deactivates the heating mat. Such temperature monitoring is based on a functioning thermal path between the heating mat and the temperature control fuse. If the adhesive connection between the temperature control fuse and the heat exchanger fails, or if small bubbles form between the heat exchanger and the heating mat, this type of temperature control fuse no longer functions. A further type of malfunction relates to local failure of the heating mat, as a result of which arcing and thus the presence of very high local temperatures can occur. While the heat exchanger comprises a metallic housing, this can, however, not prevent excessive temperatures, in particular if the heating mat becomes detached or if arcing occurs.